The invention relates to an abrasive wheel assembly, particularly for abrasive cut-off wheels of the consumable type, i.e. of the type which are used up by the grinding operation, and which are provided with a circular preferably metallic blade and abrasive segments attached to the blade and having conical or parallel lateral surfaces and plane securing plates of preferably metallic material resistant to bending. The securing plates extend into the circular blade, and the abrasive segments are securable to and removable from the circular or polygonal periphery of the circular blade, whereby the portion of the securing plate embedded in the segment adheres to the segment over the entire area of contact.
The invention particularly relates to segments for a grinding or abrasive wheel operable to economically groove or cut workpieces having a large cross section.
Though abrasive or cut-off wheels with the above-mentioned structure are already known, at least in literature, so-called one-piece wheels have generally been used up to now in cutting metallic workpieces. In one-piece wheels of this kind the entire wheel consists of grain bonds, reinforcing means and fillers without being provided with an actual blade, made, for instance, of metal.
The manufacture of such wheels with a diameter of more than 800 mm involves considerable difficulties and in addition such cut-off wheels are economically usable only for a limited time. This disadvantage is particularly due to the fact that cut-off wheels of this kind must be relatively thick, firstly for reasons of manufacture, and secondly to be able to absorb strong centrifugal and component forces occuring in operation. However, in use only a relatively small marginal portion of the wheel may wear away. Further usage of such wheels for cutting smaller cross sections on smaller machines is obstructed by excessive material loss, the necessity of increased dynamic stresses thereby conditioning considerable overload of the engine and the machines, as well as an increase in temperature occuring in the cross section to be cut, thereby causing damage to the workpiece and the cut-off wheel.
In this connection it is to be noted that on an average the breadth of the wheel is supposed to measure 1% of the external diameter of the cut-off wheel. Accordingly, the breadth of the wheel used as the cutting surface, in the cut-off wheels which now can be built to a diameter up to 1500mm, may measure up to 15 mm. Consequently, a substantial portion of cut-off wheels now employed remains unused.
On the other hand, the cut-off wheels hitherto known provided with a reusable, for instance, metallic blade and abrasive segments securable to its periphery are not satisfactory in practice. The difficulties thereby reside in the fixing of the segments to the blade.
The operator should be able to easily and rapidly replace and secure the segments on the spot where the machine is positioned without needing auxiliary persons or means. However, the fixing has to ensure the positioning and alignment of the segments since a minor misalignment of the segments in operation may involve their breakage. In this connection the legal safety rules requiring a minimum burst speed of one and a half of the operating speed must also be considered.
An example of solving this problem has been a proposal according to which each segment is provided with a continuous metallic blade, the rim of which extends out of the segment and is securable to the blade.
It is true that this proposal solves the problems of alignment and guiding of the segments and prevents setting, but only by renouncing the good grinding qualities of the segmental abrasive wheel. The safety rules for cutting at high speed (more than 60m/s) require, however, a securing plate with a minimum thickness of 2mm. However, a plate of this kind does not wear down in operation. As a result, a segment with a continuous sheet is unusable.
Even at a lower grinding speed the usage of a wheel of this kind involves practical problems. Specifically, because of core armoring, that is because of the securing plate being continuous, the segments cannot wear down equally. But what is even more important, because of the unequal wear of the securing plate and the abrasive material and the missing homogeneity of the grinding area of the segments it cannot be prevented that several parts break out, thereby making an operation impossible, particularly in view of the safety rules in force.